The recording density of magnetic recording and reproducing apparatuses is expected to reach the order of Tbits/inch2 by the development of perpendicular magnetic recording methods and magnetic head techniques using current perpendicular to plane giant magnetoresistance (“CPP-GMR”) elements, or tunneling magnetoresistance (“TMR”) elements. However, such a high recording density would not be easily achieved by using the aforementioned magnetic head techniques since narrowing the gap between shields of magnetoresistive elements serving as reproducing elements is difficult due to many layers included therein such as antiferromagnetic layers, magnetization pinned layers, nonmagnetic layer, and magnetization free layers.
Reproducing heads using a spin accumulation effect are proposed to narrow the gap between shields. In a reproducing head using a spin accumulation effect, a magnetization pinned layer and an antiferromagnetic layer are disposed to be recessed from a surface facing a recording disk (air bearing surface (“ABS”)), a sense current is caused to flow through the magnetization pinned layer to transfer, through a nonmagnetic layer, spin-polarized electrons to a magnetization free layer at the ABS, and a non-local voltage measurement is performed at the magnetization free layer with no current flowing therethrough. Since the magnetization pinned layer and the antiferromagnetic layer are recessed from the ABS, the gap between shields can be narrowed, and a magnetoresistance effect can be obtained.
In order to achieve reproducing heads using the spin accumulation effect, the output voltage should be increased. However, the current density is said to have a limit of about 1×107 A/cm2. In order to improve the sense current, the thickness of the nonmagnetic layer should be maintained at a certain level. On other hand, in order to improve the recording density, the gap between shields should be narrowed further. Therefore, the structure for narrowing the gap between shields without reducing the output voltage is important.